CHAP. V THE ANTHOCEROTE^ 115 



genera occur in the temperate zones, but are more abundant in 

 the warmer regions, where they also reach a greater size. The 

 species of AntJwceros and Notothylas grow principally upon the 

 ground in shady and moist places, and are not well adapted 

 to resist dryness. 



A marked peculiarity of their structure is the character of 

 the chloroplasts. There is as a rule but a single large flattened 

 chloroplast in each cell, such as occurs in a good many con- 

 fervoid Algae, e.g. ColeocJicete, Stigeocloniuin, and others, but, so 

 far as I know, is found elsewhere among the Archegoniatse 

 only in certain cells of Selaginella. Simple thin - walled 

 rhizoids are formed abundantly upon the ventral surface, where 

 there are in many species curious stoma-like clefts which open 

 into cavities filled with a mucilaginous secretion, and in some 

 of which, in all species yet examined, are found colonies of 

 Nostoc which form dark blue - green roundish masses, often 

 large enough to be readily detected with the naked eye, and 

 which were formerly ^ supposed to be gemma;. 



The sexual organs are very different from those of the 

 other Hepaticae, and are more or less completely sunk in the 

 thallus from the first. While the first divisions in the 

 archegonium are much like those in the other Hepaticae, the 

 subsequent ones are much less regular except in the axial row 

 of cells, and the limits of the outer neck-cells are in the 

 subsequent stages difficult to determine, and the archegonium 

 projects very little above the surface of the thallus, even when 

 full grown. The divisions in the axial row of cells correspond 

 to those in the other Archegoniatse. 



The origin of the antheridium is entirely different from 

 that of all other Bryophytes, but shows, as will be seen later, 

 certain suggestive resemblances to that of the lower Pteri- 

 dophytes. Instead of arising from a superficial cell, as in all 

 of the former, the antheridium, or in most cases the group of 

 antheridia, is formed from the inner of two cells arising by the 

 division of a superficial one. The outer one takes no part in 

 the formation of the antheridia, but simply constitutes part of 

 the outer wall of the cavity in which they develop. 



While the gametophyte is extremely simple in structure, 

 being no more complicated than that of Aneiira or JMetzgeria^ 

 the sporophyte reaches a degree of complexity not equalled by 



^ Hofmeister (i), p. 18. 



